1. Field of the Invention
The present invention relates to a semiconductor device and a method and apparatus for manufacturing the same and, more particularly, to a Cu diffusion preventive insulating layer in an interlevel insulating film formed between a Cu interconnection and a metal interconnection on it.
2. Description of the Prior Art
In the IC manufacturing field, as the operation speed and integration degree of devices increase, the device design rule decreases. As the device feature size decreases, the interconnection size and the gap between interconnections also decrease, so the interconnection resistance and the parasitic capacitance between interconnections tend to increase.
When the interconnection resistance or parasitic capacitance between interconnections increases, the RC time constant increases, and the signal propagation speed decrease to pose a problem in increasing the operation speed of the device. The parasitic capacitance between interconnections increases in proportion to the area of the interconnections and the relative dielectric constant of an insulating film between the interconnections, and in inverse proportion to the gap between the interconnections. To decrease the parasitic capacitance without changing the device design, it is effective to decrease the relative dielectric constant of the insulating film.
In recent years, various types of interlevel insulating films with low dielectric constants, e.g., an SiOF film with a lower relative dielectric constant than that of a conventional SiO2 film, has been studied in order to decrease the capacitance between interconnections. To decrease the interconnection resistance, a technique which uses as an interconnection material Cu with a lower resistivity than that of Al conventionally used widely as the interconnection material, and products as a result of this technique have become popular.
When Cu is used as the interconnection material, since it is difficult to micropattern Cu by dry etching, a damascene interconnection structure as shown in FIG. 1 is usually used widely. A damascene interconnection is formed in the following manner. A trench is formed in an interlevel film 6, and is filled with a barrier metal 10 and Cu. Excessive Cu and barrier metal on the insulating film are removed by CMP, thus forming a Cu interconnection 12.
If an interlevel insulating film is to be formed after formation of the damascene interconnection, as Cu easily reacts with SiO2 and diffuses, an SiN film 52 is usually formed as a diffusion preventive insulating film on Cu to a thickness of about 50 nm to 100 nm in accordance with parallel-plate plasma CVD by using SiH4, NH3, and N2, and after that an insulating film 20 of SiO2 or the like is formed.
In this case, SiN not only prevents Cu diffusion but also prevents the Cu surface from being exposed to the SiO2 etching or O2 resist ashing atmosphere when, e.g., a via hole is to be formed on the Cu damascene interconnection, so it also serves as an etching stop layer for SiO2. In this manner, the SiN film 52 formed on the Cu surface must prevent Cu diffusion and serve as an etching-stop layer.
Problems to be solved by the present invention are as follows.
1. Usually, when a SiN film is to be formed on a Cu surface, as the film formation temperature is about 400 degrees of Celsius thermometer, as the substrate temperature increases, aggregation of Cu tends to occur, and the morphology of the Cu surface degrades. Hence, a diffusion preventive insulating layer in which aggregation of Cu is suppressed is necessary.
2. One of methods of suppressing aggregation of Cu is to decrease the film formation temperature. When the film formation temperature is decreased, SiN forms a low-density insulating film. If the insulating film has a low density, the etching selectivity with respect to SiO2 decreases, and the SiN film cannot serve as an etching stop layer. For this reason, a dense film for maintaining the etching selectivity with respect to the insulating film is necessary as a diffusion preventive layer.